1. Field of the Invention
The present application relates to methods and apparatuses for performing visual tests, and in particular, methods and apparatuses for performing a simultaneously multi-temporal visual test to determine a likelihood of a visual deficit in a subject.
2. Related Art
A number of methods, apparatuses, and display patterns have been proposed for performing visual tests of a subject, but none disclose the presently claimed methods and apparatuses for performing a simultaneously multi-temporal visual test to determine a likelihood of a visual deficit.
U.S. Pat. No. 6,527,391 to Heijl et al. is drawn to a typical method and apparatus for performing a computerized visual field test for identifying visual deficits. Such visual field tests typically are performed in one region of the eye at a time. They require long testing times, and are compromised when a subject fixates on the wrong portion of a display. The recording of overt responses is also problematic in certain populations, including the prelingual, the nonlingual, the elderly, and those who might intentionally or inadvertently hide their deficits.
U.S. Pat. No. 5,539,482 to James et al. is drawn to a glaucoma test using a pattern electroretinogram of a subject. The visual stimulus signals used are grating patterns, with the contrast of the signal applied to each zone modulated with a different temporal frequency. Differences between electroretinogram components for an individual zone and the expected response component for that zone indicate a change in ganglion cell function in that zone.
The use of an electroretinogram such as that proposed by James et al. for a glaucoma or vision test leads to a number of problems which are overcome by the present disclosure. An electroretinogram is highly problematic, as it requires the attachment of an electrode to the cornea or sclera of a subject, who must thus be sedated or anesthetized for the test. This limits the use of such a test to healthy populations, and demands that the test be performed in sterile environments such as hospitals. Moreover, known variations between subjects may cause the absolute comparison of any electroretinogram component to an “expected response component,” as described by James et al., to be inaccurate or insufficiently sensitive. A still further problem is that the electroretinogram only identifies deficits in the retina, and not in all the various other regions of the visual field, such as along the optic pathway or even in the brain.
U.S. Pat. No. 6,840,622 to Kutschbach et al. also discloses the use of an electroretinogram for determining the topography of reaction signals in the eye, and is highly problematic for all of the above reasons.
U.S. Pat. No. 6,477,407 to Klistorner et al. is drawn to the use of a multifocal pattern visual evoked potential (VEP) for use in detecting visual field loss. However, this patent does not disclose, teach, or suggest a simultaneously multi-temporal visual display. This patent is also drawn to the identification of visual field loss by comparing electrical brain activity acquired over two or more regions of the brain, and not by comparing components of VEPs acquired with as little as one electrode pair. The uses of phase, frequency, and magnitude components, compared to each other and to corresponding display factors, are also not disclosed.
U.S. Pat. No. 6,688,746 to Malov is drawn to a method of providing a visual reaction map of at least part of the visual eye field of a subject. However, this patent does not disclose, teach, or suggest comparing components of VEPs acquired with as little as one electrode pair. The uses of phase, frequency, and magnitude components, compared to each other and to corresponding display factors, are also not disclosed.
U.S. Pat. No. 7,006,863 to Maddess is drawn to a method and apparatus which use sparse stimuli to assess neural function. Temporal sequences of stimulus conditions are presented infrequently against a frequent baseline null stimulus condition. However, this patent does not disclose, teach, or suggest a simultaneously multi-temporal visual display, nor does it disclose, teach, or suggest comparing components of VEPs. The uses of phase, frequency, and magnitude components, compared to each other and to corresponding display factors, are also not disclosed.
Thus, there remains a need for a simplified, simultaneously multi-temporal visual test that readily determines the likelihood of a visual deficit in a subject.